Field
This application relates to calcium-containing bone grafting materials.
Background Information
Current synthetic calcium-containing bone grafting materials used clinically include calcium sulfate, calcium carbonate (coral-based), and various calcium phosphate compounds (e.g., tricalcium phosphate, hydroxyapatite). The synthetic calcium-containing materials have the disadvantage of either resorbing too fast (e.g., calcium sulfate) or too slow (e.g., hydroxyapatite), which would negatively impact bone growth and regeneration.
Carbonate apatite is the mineral structure of natural bone. Unlike the highly crystalline structure of hydroxyapatite, carbonate apatite in bone has a lower degree of crystallinity. The lower degree of crystallinity allows the bone to turnover and remodel in vivo, particularly under the influence of mechanical stress conditions. If the mineral can be isolated from natural bone without significantly changing its structure, it would be a more suitable bone grafting material.
Methods for preparing mineral from natural bone include those using organic solvents (e.g., ethylenediamine) under reflux conditions (see, e.g., U.S. Pat. Nos. 2,938,593; 5,167,961; and 5,417,975), and those using heat treatment at a temperature generally higher than 900° C. (see, e.g., U.S. Pat. No. 4,654,464). These methods have various disadvantages, such as generating toxic solvent waste, altering the structure of the bone mineral, and making bone mineral that causes tissue reactions. See, e.g., Gardner, A. F., J. Oral. Surg. Anesth. Hosp. Dent. Serv., 1964, 22:332-40.
There is a need for a method that generates commercial quantities of highly porous, biocompatible, and bioresorbable carbonate apatite from natural bone without significantly changing the structure of the mineral phase and that will not generate toxic waste.